Alarm bells

[thedoc01]

Hi all , to the point> lost top gears been running car trying to adjust cables etc no avail.coolant boiling over to the point its blowing back from the header tank ,water draining from overflow tube when car sits. brownish substance on cap but oil and atf seem fine. Am i in the dreaded head gasket sector? Could this be the reason i have no top gears as i read somewhere about oil cooled gearbox oil and such making gear changes non existent. I have put too much into the old gal to bail now so someone please enlighten me as to if this could be my gearbox issue and if so how much more will i have to hide from the missus?

 

[Tinkerer]

Let the car stand (overnight) and go cold, next morning take the radiator cap off the release all pressure and then put it back on tight, then start the engine and run for about 5 mins but not to get the engine hot, turn off and then release the radiator cap carefully, if there is pressure in the system at this stage then your head gasket may well be gone. Can't help with the gearbox i'm afraid but hopefully someone who can will be along shortly.